Monday, June 6, 2011

Flagging dangles (free end points) with gvSIG

It is quite straightforward to flag dangles (or free end points) using the topology tools in gvSIG. Simply create a new topology rule to check for dangles on a linear layer(s), then run the validation. All the dangles would be flagged out as error points on the map.

To illustrate:

  1. Run gvSIG OADE 2010. Load and display a line layer e.g. lines.shp in the Map View.

    Note: the blue rectangles indicate the end points of the line segments for illustration purposes only.
  2. Select Tools | Topology | Create Topology.

    The Create topology wizard appears.

  3. Click Next.

  4. In the Topology name field, type in a string e.g. dangles.
  5. In the Cluster tolerance field, key in a value e.g. 1.
  6. In the Maximum number of errors, key in a value e.g. 20.
  7. Under the Layers to include in topology list, toggle on a layer e.g. line.shp. Click Next.

  8. Click Add.

    The Topology rules dialog box appears.

  9. In the Topology rule drop down list, choose All line geometries of A must be free of dangling nodes. Click OK.

    The rule is added to the list.

  10. Click Finish.

    A new group named dangles is added to the TOC (legend).

  11. In the legend, click the group dangles.
  12.  Select Tools | Topology | Validate Topology.

    A new layer dangles_error is created under the dangles group. The dangles are flagged in the Map View.

  13. Optional. Click on the dangles_error layer in the legend. Select Layer | Show Attribute Table.

    The Table: Attribute table:dangles_error dialog box appears.

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